1. Field of the Invention
The present invention relates to a hot swap circuit module, and particularly to a hot swap circuit module for a switch.
2. Description of the Related Art
Hot swapping is a useful functions for inserting a hard disk drive, an interface card into a system, and removing a device from the system when the system is hot. Hot swapping saves time for shutdown and rebooting. It is very useful in managing and maintaining a network system. There are many logic circuits and interface cards electrically connected together in a typical network system. Were it not for hot swapping, it would take much time to save the status data of the network system to shut down the network system. Similarly, it also takes much time to assert the initial value of the network system. For example, when a switch is shut down to replace a switch module, the network is disconnected for a long time and the transmission efficiency of the network is reduced. Thus, hot swap design is very important in a switch.
In order to reduce the impact of a hot swap, the prior art usually requires additional circuits. FIG. 1a illustrates the disturbance of the bus signal caused by a hot swap. FIG. 1b illustrates a structure of a hot swap bus. A bus 60 is connected to a device 61 through a signal line 63, to a device 62 through a signal line 64, and a device 65 is going to connect to the bus 60. The device 61, 62, and 65 all comprise a driving signal line DRV and receiving signal lines RCV and, there-upon uncharged capacitance loads CLx, Cly, and CLz to ground. When the device 65 is inserted into the connector connected to the bus 60, the bus 60 is instantaneously shorted to ground by a capacitance load CLx , and a disturbance signal 53, which is relative to a quiesced signal level 51, occurs and finally recovers to the quiesced signal level. If the disturbance signal 53 is not processed by a specific circuit, it will result in malfunction. FIG. 2 illustrates a conventional hot swap structure. The conventional hot swap structure is implemented by a separate live insertion bus controller (LIBC) 70, which comprises an interface 71 coupled to a system bus 72, and a system bus controller (SBC) 73. The separate live insertion bus controller 70 can be integrated into the system bus controller 73. The feature card 74, 75, 76, and 77 can be inserted into the connectors of the system bus 72. The live insertion bus controller 70 manages the control of the system bus 72 by a interface 78 and the system bus controller 73.
When a feature card is inserted, the live insertion bus controller 70 acquires accesss to the system bus 72 through the interface 78 with the system bus controller 73. After the access to the system bus 72 has been acquired by the live insertion bus controller 70 and the live insertion bus controller 70 has taken over the control of the system bus 72, the live insertion bus controller 70 drives a subset of the control signal of the system bus 72. The control signal of the system bus 72 is not affected by the disturbance signal resulting from the live insertion. When the live insertion bus controller 70 is informed that the live insertion process has been completed, the system bus controller 73 again acquires control of the system bus 72. The same procedural steps are performed in case of removal of a feature card.
Therefore, a mechanism is needed to define and control the start and end time for the live insertion bus controller 70 to become master of the system bus 72. The feature card 74, 75, 76, and 77 must generate an indicate signal which informs the live insertion bus controller 70 of the state of live insertion of the feature card. The indicate signal is generated by long and short stagger length contact pins for the electrical connection between the feature card and the system bus. As shown in FIG. 3, the feature card 74 comprises the pins 55, 56, and 57. The point of time, when the feature card 74 is about to be inserted or has been completely removed, is indicated by the pin 55. Correspondingly, when the feature card 74 has been completely inserted or is about to be removed, is indicated by the pin 57.
There are some disadvantages in conventional hot swap. First, special pins and connectors are required for detecting insertion or removal of devices. Usually, the device can not comprise special pins and connectors. Second, an additional bus controller is necessary to take over system bus, to build up additional signal path. The hot swap structure is more complex. Therefore, a hot swap structure for general interface is needed.
It is therefore an object of the present invention to provide a circuit system with a hot swap capability which does not require special pins or circuits and provides stability and efficiency.
To achieve the above objects, the present invention provides a hot swap circuit module. According to the embodiment of the invention, the hot swap circuit module includes a circuit board and a latch.
A hot swap circuit module is used for a circuit system having a backplane. The circuit board has plural pins for inserting into the backplane.
The latch, disposed on the circuit board, has a data input terminal for receiving an important signal, a control terminal for receiving a clock signal for latching the important signal.
When the hot swap circuit module is removed from the backplane or inserted into the backplane, the clock signal does not trigger such that the important signal is not output from an output terminal of the latch. The configuration of the circuit system is not affected by the hot swap action. The hot swap capability allows the replacement or addition of pluggable module without also requiring the circuit system to be powered down. This in turn enhances the continuous availability characteristics of the circuit system by allowing continued operation during service, change, or hardware upgrade operations.